I have an '89 trooper and when the blower switch is moved to the off position it still blows air (vent). Other problem I am having is there is no defrost. When I move the slider to defrost, I hear the flap moving but no air blows. I checked underneath the dash and verified that the controls on the driver side of the black box (that control the flap) are moving. I notice that when I put on defrost the flap moves up and then closes shut (vent air). Are these two problems related? Any suggestions? Oh yea, A/C system has a leak so compressor is not working, but i didn't think this would have any effect on the controls and the blower fan still blowing when the switch is off. Any suggestions?

I know when I move mine to the off position it still blows air, just very slowly, if I rember the control is just differnt resistors to slow the blower motor, with no off position.
The others I don't know... mine was broken a while ago, don't remeber how I fixed it though.

Check your fuse for the compressor.
The solinoid that controls the vacuum that operates the flapper doors is on the same fuse as the compressor.
Also, check outside where the A/C lines enter the firewall and make sure the vacuum line is attached to the nipple that's between the A/C lines at the firewall.

I see the nipple between the a/c lines but which vacuum hose goes there?? I have been wondering what that nipple is for for the last 1.5 years! I know I have a leak in the a/c system, I am going to have it converted to r134 in a few months. I will double check the fuse on the compressor as well. Let me know where the other end of the vacuum hose connects too. Thanks

There is supposed to be a vacuum hose that goes from an air nipple on the air plenum. It's about 1 inch behind where the throttle body bolts to the plenum. That nipple should have a vacuum hose coming off and going to that nipple on the firewall. If you have cruise control, you might have a T-fitting that splits off and goes over to the acuator, as both run off that same vacuum port line.

Litnin, I see the nipple on the firewall between the two A/C hoses and I see the hose on the throttle body but it goes directly to the cruise control(no tee). The nipple looks almost too small to fit any of the vacuum lines tightly. Is it possible that nipple was not used for my model year ('88)? I honestly cannot remember ever seeing a vacuum hose on that nipple. Still trying to get this squared away. Thanks for your input.

M

That nipple is where the switching solinoids inside the truck (behind the glovebox) get their vacuum to open/close the doors. You should have a ported vacuum line going to that nipple. It really doesn't matter where you pull the ported vacuum from, but it was T'd off the cruise control hose from the factory.

Here's a pic for you: